I thought it would be a good investment as I was doing more in the area of
mixing and matching motors, props, and the like. It is small and simple to
use so I put it in my field box. It wasn't long before it started to show
its value.

We were flying one afternoon when one of the club members felt he was not getting
good performance from a new plane he had built. I put he wattmeter on the
plane and determined he was pulling about 9 amps. Turned out the pack he
was using really was not up to the load and the voltage was dropping off
excessively. As a result he was not getting the RPM out of the prop that he
expected. Problem discovered and cause identified in a few seconds. He
needed stronger battery packs.

A few weeks later we did the same thing with another plane. There was a
concern that the LiPo being used might be getting over worked. However the
Wattmeter showed that it was working well within its rated capacity. Flying
went on with confidence.

I recently purchased an Easy Glider Electric from another club member. He
had upgraded the motor from the stock speed 400 to a brushless, a 27 amp ESC
and was using 2 cell 2100 MAh LIPOs. I bought the whole package.

The plane flies very nicely on the 2 cell packs, but I had a 3 cell pack
that I thought I might add to the rotation and REALLY boost the power. The ESC could handle 3 cell LiPo so I did not see a problem. I assumed the system was probably running at about 18 amps which was within the rating of this pack. Should be a good fit.

Fortunately before I tried it in the plane I put the watt meter on the
system. I was surprised to see that the system was running at 26 amps on the 2 cell lipo packs. That was much higher than I had expected. It turned out that the 2 cell packs were an excellent match for the motor and speed control. The amp load was well within the specs of the 2 cell packs being used and the plane flew very nicely on this combo.

If I had blindly put a 3 cell pack in there I would have pushed well past
the ESC's 27 amp rating and probably burned out the speed controller. Or,
in the case of my 3 cell pack, it would probably have pushed over 30 amps
into the system due to the higher voltage, but it was not rated for that
high of an amperage and would probably have had a short life working at that
level. I would have thought it was just a crummy battery pack but in fact I
would have been over working it.

Operating in the blind I would have ruined the ESC, or the pack, or both. A
very expensive mistake. Certainly more than the cost of the watt meter. It
had just paid for itself.

A few days ago I pulled out my old Electrajet to prepare to sell it. I had
purchased it almost 3 years ago, but had never really been happy with the
plane and my interests have turned more toward gliders and slow flyers
rather than a pusher jet. When I purchased it I also bought some cells and
made up some 8 cell packs. However it really didn't seem to have the zip I
thought it should. I just attributed it to the speed 400 motor and the
plane being too heavy.

I put the watt meter on the motor/battery combo. The motor sounded about as
I had recalled. When I checked the meter, low and behold, those 8 cell
packs were duds! They were 9.6V 8 cell 1000 MAh packs rated for 10C. At
rest, fresh off the charger they were reading 11 volts, but when I hooked
them up they were both dropping to 7 volts while delivering 9 amps. That is
way too much drop! The problem was not the plane or the weight of the plane
but the quality of the cells I had used.

I tried one of my 15C Lipo packs and that held voltage well, delivering 13
amps. The motor screamed! Now that was more like what I had expected.
Hummm, maybe I won't sell it after all. I just need to put better battery
packs in it.

I also tried a 1000 MAh 2 cell lithium pack that is rated at 10 C. The
voltage sagged to 6.6 volts almost immediately. The motor ran but I was
clearly over stressing the pack. This pack would have been ruined in very
few flights if I had used it to fly the plane regularly.

I share this story only to help you understand that, without a watt meter,
or the use of a multi meter with knowledge and skill, we are working in the
blind. We really don't know what is happening in our power systems.

WHO NEEDS A WATT METER?

While the watt meter is a nice to have, some people don't need one. If you
are buying RTF planes, or ARF or kit planes and are using the manufacturer's
supplied motor and battery packs, I would say you can be pretty confident that all
is well.

However, if you start mixing and matching motors, gear boxes, props,
controllers, battery packs and the like, you are really working in the blind
if you are not measuring the energy flow in the system. In my case, I
started making my own battery packs but I was not measuring their
performance. Now I know the true results.

There are a variety of watt meters out there. This one is easy to use and
fits nicely in my field box, but there are other good ones. If you are
going to upgrade your power systems or make up your own packs, you need a
watt meter. You can perform many of the same tests with a millimeter if you
know how to work with shunts and the like, but if you want a simple to use
tool that does exactly what you need it to do, this is hard to beat. It has
other uses too, so read the instructions, but for this use alone it paid for
itself pretty quickly.

I don't have the Watts Up meter but I do use the Astro Flight Superwattmeter. I honestly don't know what I would do without it. Like Ed mentioned, you are only guessing at what your set up is doing if you don't meter it. When I set up my Magpie AP, I originally thought I would only be drawing about 25 amps max on my 30 amp speed controller and 3S 2100 15C lipos. Thankfully, I hooked the meter up before I ever tried it and it was pulling 39 amps... WOW!!!. I immediately shut it off and switched props to bring it down to 21 amps. If I wouldn't have metered it, I would have eventually fried the ESC and possibly the motor and or battery. I now never start a new system without the meter on it the very first time it's fired up.

Great post, Ed! It should be a sticky so we can easily refer people to it.

Almost every time someone posts a request for help with an e-power system, it turns out they do not yet own a wattmeter. The solutions to most of the problems would be obvious with a wattmeter connected.

I have made up various adaptor cables and can plug my Watts Up with my Deans plugs and others JST etc. I use it in conjunction with my charger to verify correct voltage and current when charging Lipos as well for current and voltage measurements when setting up a heli or plane.
A Watt Meter and a Temperature Gauge I consider essential for electric flying. Helps to have a good volt meter as well.
Gary

Jeff,
I use them after almost every flight on a new bird in order to establish a benchmark. With a new bird I first do a static run to determine amp draw. I then set the Tx timer for 4 or 5 minutes and do my usual type of flying. I immediately measure temperatures after landing. This time of year my Lipo temps are running around 115 to 120 degrees fahrenheit after a hard bit of flying. Summer time when the temperature is in the 90's Lipos and motor get warmer. I try to keep Lipo temps below 130 degrees fahrenheit. Good throttle management goes a long way toward keeping lower temps.
Gary

Hello Ed,
Great information, and for myself the timing of finding this thread is right on que. I'm searching for all the electronic stuff I can find. I'm doing my best to learn about the workings of an electric plane. Some of this stuff which is very basic for most of the members is difficult to understand. I'm gaining on this with the help of everyone.
Thanks

When I went looking for a Watt meter a few months back I found the Hyperion E-meter which has the added benefiet of a RPM meter in the nose of it. Its also has got a 3 model memory which allows you to do tests and compare results. Saves having to write everything down. It comes with a 100A shunt and Deans connectors. I love it!

I missed this the first time around. Good write-up. I think the wattmeter is a tremendous tool. You are really working with your eyes closed if you don't have one. Watts up for me. Astroflight for my Dad. They are both very nice.

I basically use my E-meter to test max amp draw on different props to make sure I dont go over any amp limits. I also use it for getting the max RPM of a prop to make sure I dont go over the props max RPM which can be very dangerous. There is so much more that this tool can do that I cant even begin to understand. You can hook it up to your computer and download all your info to an interface, but I havent tried that yet. I cant imagine not having something to let you know whats happening with your power system. Everyone should have something.

The Medusa Analyzer Pro has every bell and whistle you could imagine - and everything can be linked to your laptop: amps, volts, watts, capacity - a temperature probe, a tachometer, a thrust cell, a digital scale............graphing capacity....! http://www.medusaproducts.com/Power-.../pa-60100R.htm

Can a wattmeter be hooked up between a battery and a charger during charging to monitor the charge? Or would it interfere with the charging process in some way? The reason I ask is, I am considering getting the Thunder Power TP535C charger (largely because it has a reasonably-priced AC power supply made specifically for it), but the TP535C has no digital readout. Could I just use the wattmeter for that?